The invention relates to a system of manufacturing and, more particularly, a method and system for improving the quality of the assemblies and sub-assemblies of an automobile.
A conventional automobile assembly line produces a variety of sub-assemblies that are integrated to form a complete vehicle. For example, typical modern vehicles, such as a sedan, have a body-in-white which is comprised of a front or engine room sub-assembly, a passenger cell sub-assembly and a trunk or rear sub-assembly. Typically, a front sub-assembly will be attached to the passenger cell sub-assembly at a first assembly station on the main assembly line. The front and passenger cell sub-assemblies are usually affixed to each other by spot welds or bolts. The rear sub-assembly is then attached to the front/passenger cell assembly at a second assembly station on the main assembly line.
The sub-assemblies themselves are typically produced on a sub-assembly line, which may or may not be at the same location as the main assembly line. A sub-assembly is typically produced by affixing, typically by spot welds, a number of components, parts or pieces (which terms, hereinafter, will be used interchangeably). For instance, the front or engine room assembly typically comprises left and right front housings (which include the left and right wheel wells and shock towers), left and right frame rails, a fire-wall or dashboard component and a radiator cradle. In a typical sub-assembly line, separate left and right front fender sub-assemblies, typically comprising the front frame rails and front housings, are formed by placing the individual components into a jig at a first weld station and spot welding these components to form separate left and right fender sub-assemblies. The left and right front fender sub-assemblies are then joined together by a dashboard component to form a U-shaped structure (when viewed from overhead). This U-shaped structure is then moved to another sub-assembly line station for the installation of the radiator cradle. Further components which form part of the engine room or front sub-assembly may also be added.
Conventionally, the components which form the sub-assemblies are themselves typically comprised of a number of folded, stamped, rolled, extruded, or hydroformed pieces which are affixed to each other to form the component. These components may be produced off-site by the vehicle manufacturer or by a supplier.
In conventional assembly lines (including sub-assembly lines), many of the assembly steps require parts to be physically stacked on top of one another and then secured to each other by, for example, welds or bolts. Each of these components is formed with a certain accuracy or tolerance. That is, a particular component, and any point on that component, is typically required to have, or be located at, certain dimensions, within a specified tolerance, (i.e. xc2x11 mm, for example). If a component to be affixed references a point or another component, the reference point also having a dimensional tolerance, the tolerance in the assembly formed by these components will be also be xe2x80x9cstackedxe2x80x9d together. That is the dimensional tolerance of the first component will be added, to some degree, to that of the second component. As more components are affixed to the assembly which reference additional points, the tolerances of the individual points are xe2x80x9cstackedxe2x80x9d to create a larger total tolerance for the xe2x80x9cstackedxe2x80x9d component.
The positioning of these components spatially and relative to one another and prior to fixation is typically accomplished through the use of jigs. By way of explanation, a jig typically has pins and templates, (or location devices, such as cavities, for example) to receive parts, and clamps, to maintain parts in position prior to welding. However, a jig typically allows some play in the positioning of the parts prior to clamping (such as xc2x10.3 mm). As a result, the use of additional jigs conventionally incurs a quality penalty. That is, for each jig used, an addition positional tolerance is conventionally incurred. As a result, in a conventional assembly line, each additional jig used to spatially hold parts together prior to welding causes the positional tolerance of that jig to be added, in some degree, to the total tolerance of the final product. Accordingly, it becomes evident that an increase in the number of components whose positional and dimensional tolerances are stacked causes the total manufacturing tolerance to increase. It is evident that as the number of xe2x80x9cstackingxe2x80x9d processes increases the total manufacturing tolerance can become quite substantial.
As is well known in the automotive industry, the demand for higher quality vehicles at a lower cost is increasing. It is not uncommon for customers to demand quality tolerances for visibly apparent quality measures, such as body panel gaps, of less than 3 mm. However, it is not uncommon for some assembly processes to have twenty or thirty welding stations using twenty, or more, positioning jigs.
Accordingly, it is desired to improve the manufacturing method by reducing the overall or total tolerance in sub-assemblies and vehicle assemblies.
According to one aspect of the invention, there is provided a method of manufacturing an assembly, wherein said assembly is comprised of a plurality of components, said method comprising: forming, from some of said plurality of components, a substantially rigid initial structure; and affixing each of said remaining components of said plurality of components to said rigid initial structure.
According to another aspect of the invention, there is provided a method of manufacturing an assembly, wherein said assembly is comprised of a plurality of components, comprising: selecting from said plurality of components, some components which can be assembled into a structurally rigid sub-assembly; forming said rigid sub-assembly from said selected components; for each remaining component of said plurality of components: referencing from said rigid sub-assembly a desired position for said each remaining component on said initial structure; thereafter, affixing said each remaining component to said rigid sub-assembly at said desired position, whereby the tolerance of said manufactured assembly is reduced.
According to another aspect of the invention, there is provided an assembly line, comprising: an initial station with means for forming a rigid initial structure from a plurality of components; at least one additional station downstream of said initial station, each of said at least one additional station having: means for referencing additional components relative to said rigid initial structure; and means for affixing each additional component to said initial structure at a position referenced by said referencing means.
According to another aspect of the invention, there is provided a method of manufacturing an assembly from a plurality of components, comprising: identifying a sub-group of components from the plurality of components upon which all other components of the plurality of components can be directly affixed; forming from the sub-group an initial rigid structure; and affixing all the other components of the plurality of components directly to the initial rigid structure.
According to another aspect of the invention, there is provided an assembly line, comprising: an initial station with means for forming a rigid initial structure from a plurality of components; a plurality of additional stations downstream of the initial station, each of the plurality of additional stations having: means for referencing additional components to the rigid initial structure; and means for affixing each additional component in abutting relation to the initial structure at a position referenced by the referencing means.
According to another aspect of the invention, there is provided a method for improving the quality of manufacture of an assembly, comprising a plurality of components, said method comprising: (a) forming at a first station, from a portion of said plurality of components, an initial rigid structure having a reference point; (b) transporting said initial structure to a downstream station; (c) positioning, at said downstream station, one or more remaining components of said plurality of components with reference to said reference point; (d) affixing said positioned components to said initial structure; and (e) repeating (b), (c) and (d) for remaining components of said plurality of components.
According to another aspect of the invention, there is provided a method of manufacturing an assembly from a plurality of components comprising: selecting a reference point on at least one of said plurality of components; positioning, spatially, said other non-selected plurality of components with reference to said selected reference point; and affixing said positioned plurality of components to form said assembly.